Salinity: Electrical Conductivity and Total Dissolved Solids

This paper presents updated technology for assessing soil salinity based on measurement of electrical conductivity. The technology has been extensively and successfully field tested, and it is sound, reliable, accurate and suited to a wide variety of useful applications. The required equipment is commercially available. The advocated instrumental methodology is practical, cost effective and well developed for all general applications. It is cheaper, faster and more informative than traditional methods of salinity measurement based on soil sampling and laboratory analysis.

Soil salinity assessment :methods and interpretation of electrical conductivity measurements

Fluxes of greenhouse gases to the atmosphere are heavily influenced by microbiological activity. Microbial enzymes involved in the production and consumption of greenhouse gases often contain metal cofactors. While extensive research has examined the influence of Fe bioavailability on microbial CO2 cycling, fewer studies have explored metal requirements for microbial production and consumption of the second- and third-most abundant greenhouse gasses, methane (CH4) and nitrous oxide (N2O). Here we review the current state of biochemical, physiological and environmental research on transition metal requirements for microbial CH4 and N2O cycling. Methanogenic Archaea require large amounts of Fe, Ni and Co (and some Mo/W and Zn). Low bioavailability of Fe, Ni and Co limits methanogenesis in pure and mixed cultures and environmental studies. Anaerobic methane oxidation by “ANME” Archaea likely occurs via reverse methanogenesis since ANME possess most of the enzymes in the methanogenic pathway. Aerobic CH4 oxidation uses Cu or Fe for the first step depending on Cu availability, and additional Fe, Cu and Mo for later steps. N2O production via classical anaerobic denitrification is primarily Fe-based, whereas aerobic pathways (nitrifier denitrification and archaeal ammonia oxidation) require Cu in addition to, or possibly in place of, Fe. Genes encoding the Cu-containing N¬2O reductase, the only known enzyme capable of microbial N2O conversion to N2, have only been found in classical denitrifiers. Accumulation of N2O due to low Cu has been observed in pure cultures and a lake ecosystem, but not in marine systems. Future research is needed on metalloenzymes involved in the newly-discovered pathway of N2O production by ammonia oxidizing Archaea, biological mechanisms for scavenging scarce metals, and possible links between metal bioavailability and greenhouse gas fluxes both in anaerobic environments where metals may be limiting due to sulfide-metal scavenging.

/pdf/trace-metal-requirements-for-microbial-enzymes-involved-in-222mkgz0r7.pdf

Trace Metal Requirements for Microbial Enzymes Involved in the Production and Consumption of Methane and Nitrous Oxide

When studying metal sorption by soils, the potential influence of environmental and solution parameters on the experimental systems cannot be ignored. Characteristics of the soil mineral surfaces are the final determinative factors in whether a metal ion will be sorbed, but soil-solution composition affects both mineral surface properties and whether the metal ions will be in forms that can react with the surfaces. Examples of factors affecting sorption of metals by soil surfaces include ionic strength, cations, anions, and/or organic ligands present in solution, solution pH, and solution metal concentration. In addition, sorption will be affected by external factors such as pressure, temperature, soil/solution ratio, and the manner in which soils to be studied are sampled and stored before investigation. To date, there has been little attempt to standardize experimental protocol, so results obtained using varied systems in different laboratories cannot be readily compared. An initial suggestion that all sorption studies include at least one treatment meeting minimal standards of ionic strength (0.01), background electrolyte (NaNO 3 ), pH (between 5.5 and 6.0), and temperature (25 ± 3°C) is presented as a first step toward enabling improved ability to make interlaboratory comparisons.

An assessment of environmental and solution parameter impact on trace-metal sorption by soils

Soil interstitial waters are an extremely important facet of many environmental studies. The biogeochemical cycles of important nutrients, metal migration across the landscape, and pollutant movement to groundwater are highly affected by the water flow characteristics in soils and sediments. The purpose of this review is to evaluate the various soil solution sampling techniques. There is no single device that will perfectly sample soil solution in all conditions encountered in the field; hence a critical literature review on the different soil solution samplers is given. The differences among the various soil solution samplers and their relative advantages and limitations are discussed. The problems involved in using these samplers are assessed and plausible solutions are presented.

Douglas L. Miles

Papers

Extraction and chemical analysis of interstitial water from soils and rocks